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"American Sniper" earned six Oscar nominations, including best picture

(CNN)Documentary filmmaker Michael Moore pronounced that "snipers aren't heroes" in a tweet on Sunday as "American Sniper," the Oscar-nominated biopic of a former Navy SEAL and sharpshooter, won the weekend box office.

The "Fahrenheit 9/11" and "Bowling for Columbine" director later expanded on his remarks, saying: "But if you're on the roof of your home defending it from invaders who've come 7K miles, you are not a sniper, u are brave, u are a neighbor."

My uncle killed by sniper in WW2. We were taught snipers were cowards. Will shoot u in the back. Snipers aren't heroes. And invaders r worse

Moore has long been a staunch advocate for stricter gun control laws in the U.S., and his statements are known to court controversy.

His latest comments quickly prompted backlash. Former U.S. House speaker and CNN contributor Newt Gingrich invited Moore to spend some time with terrorist cells overseas, then weigh in on the value of snipers.

Michael Moore should spend a few weeks with ISIS and Boko Haram. Then he might appreciate@AmericanSniper. I am proud of our defenders.

The movie, starring Bradley Cooper and directed by Clint Eastwood, earned $105 million in weekend ticket sales and nabbed six Academy Award nominations last week, including best picture. The box office take trumped previous records for a January opening and is expected to grow on Monday as moviegoers enjoy another day off for the Martin Luther King Jr. holiday weekend.

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Moore isn't the only one in Hollywood taking aim at the film: Actor Seth Rogen equated the war drama to a Nazi propaganda film shown in Quentin Tarantino's "Inglourious Basterds."

American Sniper kind of reminds me of the movie that's showing in the third act of Inglorious Basterds.

"American Sniper" is based on the best-selling memoir of the same name by Chris Kyle. Kyle served four tours in Iraq with the Navy SEALs and is lauded as "America's deadliest sniper." He was not without controversy of his own, including disputed claims in his book that he punched former Minnesota Gov. Jesse Ventura and killed two armed carjackers. Kyle was shot and killed by a former Marine in 2013.